If you follow investment information on social media, you’ve seen a variant of the following chart many times: U.S. stock prices are very high (as measured by the Shiller CAPE in this case), and we are near the right side of the chart today.  The intended message is that we are sure to have terrible U.S. stock returns for the next 10 years.  The R-squared value of 79% means that the correlation is strong.  All the points are close to the line that’s been fitted to them. But what’s the reality here?  Are we doomed?  The first thing to observe is that the chart covers 39.5 years.  That's close to 4 decades.  Doesn’t that mean there should be only 4 dots?  What they’ve done is collect monthly data so that there are 475 points.  But that means that one point overlaps with the next in 119 out of 120 months. With so little data, statistics are completely unreliable.  It could be that the correlation is much weaker and we just happen to be in a...